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Harness Test Advisor

Graph-based test selection. Answers: "I changed these files — what tests should I run?"

When to Use

• Before pushing code — run only the tests that matter
• In CI — optimize test suite execution order
• When a test fails — understand which changes could have caused it
• When

  on_pr

  triggers fire
• NOT for writing tests (use harness-tdd)
• NOT for test quality analysis (out of scope)

Prerequisites

A knowledge graph at

.harness/graph/

enables full analysis. If no graph exists, the skill uses static analysis fallbacks (see Graph Availability section). Run

harness scan

to enable graph-enhanced analysis.

Graph Availability

Before starting, check if

.harness/graph/graph.json

exists.

If graph exists: Check staleness — compare

.harness/graph/metadata.json

scanTimestamp against

git log -1 --format=%ct

(latest commit timestamp). If graph is more than 10 commits behind (

git log --oneline <scanTimestamp>..HEAD | wc -l

), run

harness scan

to refresh before proceeding. (Staleness sensitivity: Medium)

If graph exists and is fresh (or refreshed): Use graph tools as primary strategy.

If no graph exists: Output "Running without graph (run

harness scan

to enable full analysis)" and use fallback strategies for all subsequent steps.

Process

Phase 1: PARSE — Identify Changed Files

1. From diff: Parse

   git diff --name-only

   to get changed file paths.
2. From input: Accept comma-separated file paths.
3. Filter: Only consider

   .ts

   ,

   .tsx

   ,

   .js

   ,

   .jsx

   files (skip docs, config).

Phase 2: DISCOVER — Find Related Tests via Graph

For each changed file, use graph traversal to find test files:

1. Direct test coverage: Use

   get_impact

   to find test files that import the changed file.

   get_impact(filePath="src/services/auth.ts")
   → tests: ["tests/services/auth.test.ts", "tests/integration/auth-flow.test.ts"]
   

2. Transitive test coverage: Use

   query_graph

   with depth 2 to find tests that import files that import the changed file.

   query_graph(rootNodeIds=["file:src/services/auth.ts"], maxDepth=2, includeEdges=["imports"], bidirectional=true)
   

3. Co-change tests: Check

   co_changes_with

   edges for test files that historically change alongside the modified files.

Fallback (without graph)

When no graph is available, use naming conventions, import parsing, and git history:

1. Tier 1 — Filename convention matching: For each changed file

   foo.ts

   , search for:

   • foo.test.ts

     ,

     foo.spec.ts

     (same directory)

   • __tests__/foo.ts

     ,

     __tests__/foo.test.ts

   • Test files in a parallel

     tests/

     directory mirroring the source path
2. Tier 2 — Import-linked tests: Parse test files' import statements (grep for

   import.*from

   in

   *.test.*

   and

   *.spec.*

   files). If a test file imports the changed file, it belongs in Tier 2 (if not already in Tier 1).
3. Tier 3 — Co-change correlated tests: Use

   git log --format="%H" --name-only

   to find test files that frequently change in the same commit as the target file. Files that co-change in >2 commits are co-change correlated.
4. Rank: Tier 1 = direct filename match, Tier 2 = import-linked tests, Tier 3 = co-change correlated tests. Output the same tiered format as the graph version.

Fallback completeness: ~80% — naming conventions and imports catch most mappings; misses dynamic imports and indirect coverage.

Phase 3: PRIORITIZE — Rank and Generate Commands

Organize tests into three tiers:

Tier 1 — Must Run (direct coverage): Tests that directly import or test the changed files. These are most likely to catch regressions.

Tier 2 — Should Run (transitive coverage): Tests that cover code one hop away from the changed files. These catch indirect breakage.

Tier 3 — Could Run (related): Tests in the same module or that co-change with the modified files. Lower probability of failure but worth running if time permits.

Output

## Test Advisor Report

### Changed Files
- src/services/auth.ts (modified)
- src/types/user.ts (modified)

### Tier 1 — Must Run (direct coverage)
1. tests/services/auth.test.ts — imports auth.ts
2. tests/types/user.test.ts — imports user.ts

### Tier 2 — Should Run (transitive)
3. tests/routes/login.test.ts — imports routes/login.ts → imports auth.ts
4. tests/middleware/verify.test.ts — imports middleware/verify.ts → imports auth.ts

### Tier 3 — Could Run (related)
5. tests/integration/auth-flow.test.ts — same module, co-changes with auth.ts

### Quick Run Command
npx vitest run tests/services/auth.test.ts tests/types/user.test.ts tests/routes/login.test.ts tests/middleware/verify.test.ts

### Full Run Command (all tiers)
npx vitest run tests/services/auth.test.ts tests/types/user.test.ts tests/routes/login.test.ts tests/middleware/verify.test.ts tests/integration/auth-flow.test.ts

Harness Integration

• harness scan

  — Recommended before this skill for full graph-enhanced analysis. If graph is missing, skill uses naming convention and import parsing fallbacks.

• harness validate

  — Run after acting on findings to verify project health.
• Graph tools — This skill uses

  query_graph

  ,

  get_impact

  , and

  get_relationships

  MCP tools.

Success Criteria

• Tests prioritized into 3 tiers (Must Run, Should Run, Could Run)
• Executable run commands generated for quick and full test runs
• Coverage gaps flagged for changed files with no test coverage
• Report follows the structured output format
• All findings are backed by graph query evidence (with graph) or systematic static analysis (without graph)

Examples

Example: Selecting Tests for a Services Change

Input: git diff shows src/services/auth.ts and src/types/user.ts modified

1. PARSE    — 2 changed files identified (both .ts)
2. DISCOVER — get_impact(filePath="src/services/auth.ts")
              query_graph with depth 2 for transitive tests
              Tier 1: auth.test.ts, user.test.ts (direct imports)
              Tier 2: login.test.ts, verify.test.ts (one hop away)
              Tier 3: auth-flow.test.ts (co-change history)
3. PRIORITIZE — 5 tests across 3 tiers

Output:
  Tier 1 (must run): 2 tests
  Tier 2 (should run): 2 tests
  Tier 3 (could run): 1 test
  Quick command: npx vitest run auth.test.ts user.test.ts login.test.ts verify.test.ts
  Coverage gaps: none

Rationalizations to Reject

Rationalization	Reality
"Only the Tier 1 direct tests matter -- Tier 2 and Tier 3 are probably unnecessary"	Tier 2 tests catch indirect breakage one hop away. A change to auth.ts breaks login.ts which breaks login.test.ts. Skipping Tier 2 misses exactly the regressions hardest to debug.
"The changed file has no tests, but that is not my concern -- I just advise on which tests to run"	Coverage gaps must be flagged. When a changed file has no test coverage, the advisor reports it. Silently producing an empty test list gives false confidence.
"The graph is stale but I will use it anyway since some data is better than no data"	If the graph is more than 10 commits behind, refresh before proceeding. Staleness sensitivity is Medium for test advisor.

Gates

• Graph preferred, fallback available. If no graph exists, use naming conventions, import parsing, and git co-change analysis to identify relevant tests. Do not stop — produce the best test selection possible.
• Always include Tier 1. Direct test coverage is non-negotiable — always recommend running these (whether found via graph or naming conventions).

Escalation

• When changed file has no test coverage: Flag as a gap: "No tests found for src/services/auth.ts — consider adding tests before merging."
• When Tier 1 has >20 tests: The changed file may be a hub. Suggest running Tier 1 in parallel or splitting the file.